The Doom novels are a series of four officially licensed books, written by Dafydd ab Hugh and Brad Linaweaver. They were released by Pocket Books between June 1995 and January 1996. They were reissued in 2005 with new cover paintings.
The four titles, Knee-Deep in the Dead, Hell on Earth, Infernal Sky, and Endgame, comprise a continuing narrative centering around Space Marine Flynn "Fly" Taggart and a ragtag band of human survivors. All are written from a first person perspective, usually with Flynn Taggart as the narrator. Ever since their publication, some Doom fans have insisted that "Flynn Taggart" is the Doomguy's real name, though id Software has never confirmed it.
 Knee-Deep In The Dead
The first book, based on the events of the first Doom game, flows with the continuity of the three episodes, mentioned below. It opens with a prologue in the Middle Eastern country of Kefiristan. Fox Company leader Lt. Weems orders his men to open fire on civilians. Flynn "Fly" Taggart, the "Doomguy", attacks him.
Before he can be sent for court martial, however, Fox Company is called to the UAC research facility on Phobos to deal with a disturbance. Fly is kept prisoner by two Privates while the rest are sent off. This may be Fly's saving grace, as Fox Company is wiped out by the invading forces. Escaping, Fly encounters several zombies, then a run-in with an Imp (Knee-Deep in the Dead).
Moving deeper into the complex, Fly finds more monsters, as well as "A.S." arrow marks on the walls - PFC Arlene Sanders, his best friend, has survived and is leaving him directions. Ultimately, Fly reaches the two Barons, defeats them, and is transported to Deimos Base, completely naked (The Shores of Hell). On Deimos, he finds Arlene, regains clothes and weapons, and the two eventually find the Cyberdemon and defeat it. Teleported again, the two find themselves inside a gigantic fleshy enclosure, and field-strip corpses for clothes and weapons once more (Inferno).
Here, they meet Bill Ritch, a UAC computer programmer whom the Spider Mastermind captured and tried to interrogate. The three make their way through this complex, ultimately defeating the Spider Mastermind, at the cost of Bill Ritch's life.
Returning to the surface, they find they are still on Deimos, which has been moved to Earth orbit. And the giant dome that holds in the oxygen has cracked. Worst of all, they can see explosions all over Earth's surface - the invasion has already reached Earth.
 Hell on Earth
The second book opens right as the first ends, with Fly and Arlene stranded on Deimos, in Earth's orbit and the oxygen leaking out of the base. Fly gets the idea to build a shuttle craft to carry them to Earth - a risky, improbable plan, and while they have the parts from "mail tube" unmanned shuttle parts, their experience lies in the fact that Fly once built a car out of spare parts.
Over the next month, the two build their craft, but as the oxygen runs low and they start to hallucinate and run out of food, they fly their shuttle, managing to survive the trip, eventually landing several miles away from Salt Lake City. A several days' walk leads them to the city, and the truth - humanity is an endangered species. SLC is one of the few human resistance strongholds, as the Mormons had a survival plan and years worth of supplies for such an event.
Arlene expresses displeasure over their surroundings, as her brother had converted to Mormonism during his own downward spiral in life. Fly makes things worse when he contacts Marine HQ. As it turns out, world governments turned traitor to the aliens, as did their militaries. Within hours, armed forces from the Marines, FBI, Army, ATF, and IRS (a "revenue collection" armed branch) attack the city.
The President of the Twelve, displeased at Fly and Arlene's failure, offer them a chance to make amends - lead a team into Los Angeles, recover vital information, disable the aliens' shields, and fly the information to a Marine resistance center in Hawaii. With them will be Albert Gallatin, an ex-Marine sniper and converted Mormon, and Jill Lovelace, a fourteen-year-old former computer hacker who lost her parents in the invasion.
The book follows their trip west. On the trip, Arlene falls in love with Albert despite his religion. Jumping a train headed west, the team kills a Spider Mastermind and a Cyberdemon and recover their human hostage - Ken, a young man with numerous computer implants in his body. Reaching LA, they find that the chemical brew that turns corpses into zombies is made by stoners and other drug addicts, those allowed to remain alive by the aliens for turning traitor.
Having determined Ken to be the information they need, they reach the airport. Albert is burned severely by an Imp fireball, but is luckier than Bill Ritch and survives. Albert and Jill remain behind to fly the plane to Hawaii while Fly and Arlene head to the Disney Building to disable the massive force shield. They succeed, but a gathering of monsters has them trapped. But Arlene has an escape plan...
 Infernal Sky
The book starts with a disturbing prologue featuring a woman and her son, who is missing an arm and is considered a war veteren, who are hiding out in a basement after the invasion. The son asks "why are there demons?", which creates a flashback to the woman's family being devastated by the monsters. Her husband had been killed by a Spider Mastermind, and in her terror she called out to him, which provoked the Mastermind's attention. It goes after them and catches her daughter, killing her horribly. The woman then answers her son that the monsters now roaming the Earth are not demons as they can be killed. She then claims to have hope that heroes will come to save them, and the two of them stare out into the night sky...
Meanwhile, Fly and Arlene are resting comfortably in Hawaii, along with Albert and Jill at the final Marine base. Fly and Arlene both tell their own version of how they escaped Los Angeles. It is here that Fly is promoted to Sergeant and Arlene to Corporal, and without the need for a chain of command or red tape, the Marines wipe Fly's record clean of his assaulting a superior officer.
Albert and Jill also learn bad news - Salt Lake City has been nuked. And the war is about to take a turn, as the military has decoded a signal sent from an alien race warning of the attacks, and giving coordinates to find help. The mission entails a return to Phobos, and activating a gate to send a team to parts unknown.
Meanwhile, Ken, the "cyber mummy" from the previous book, has had surgery and is awake, but his implants are left functioning to tap into the enemy systems. But Ken also reads into Marine plans, and he does not like the plans he hears of the future.
Under a new CO that comes off as a stubborn "by the book" type, Captain Hidalgo, Fly, Albert, and Arlene prepare to head back to Phobos - which will require a return to Los Angeles to steal a shuttle. No easy task, and Jill is needed to infiltrate - but an escape plan is set for her on her own. And to further complicate matters, Albert proposes to Arlene.
Securing the shuttle, the flight leaves, a six week long long trip to Phobos. Jill, left behind, misses her escape, left in enemy territory. In perhaps the most haunting scene of the book, Jill is forced to kill two human traitors with poison gas.
Back on Phobos, the team eventually reaches the Gate, and are sent off to a strange facility where they meet many other aliens, their allies against the demons. The chief representatives, the Klave serve as their liaisons. Few details are gained, but it seems Earth is another stop along a six million year war against the two alien sides. And humans have angered the demons, as humans, it seems, are the only species that actually dies.
It is explained that, for most races, when the body dies, the soul remains behind until a birth gives them a new body. Otherwise, the dead are arranged in theaters and entertained in the meantime. Humans do not work this way, they die.
The plan is simple - fly to the alien invader homeworld- called the "Freds" by Marine HQ, and take the war to their front door. But without faster than light travel, while they will experience the trip in weeks, the actual trip will be twenty years each way. And when an accident leaves Albert unable to go, Arlene marries him - knowing when she meets him again, he will be in his sixties.
To complicate matters, the trip is interfered when a large spaceborne creature attacks their ship. They fight it off, but extensive damage forces them to a nearby planet to another gate. Transporting, the gate malfunctions as Fly accidentally telefrags Hidalgo, forcing Fly to kill him and leaving him and Arlene alone with Sears and Roebuck, their two Klave escorts. And they are trapped on a Fred ship. This leads to Fly experiencing a berserker rage, leading them into battle; with no clothes or weapons due to the Gate transport, they have to fight bare handed, and end up killing the Fred and taking the ship.
But this ship is not as fast. It may be on a direct course for the Fred homeworld, but at their rate of speed, they will take an eight week trip - or, in actual years outside of their travel, two hundred years.
The book ends with an epilogue written/spoken by Arlene, where she laments the turn of events and knowing that she will never see Albert again. She is saddened by her loss, but understands that without the berseker fury Fly had gone through, they would not have survived the battle at all. Still, she remains distant from him, the wound still fresh. All she and Fly can do is sit on the opposite ends of the ships main chamber and stare off into the compressed, colored disc of stars, wondering what will happen to the Earth when they return.
Aboard the Fred ship, Arlene sinks into a deep despair over knowing she will never see Albert alive again, which makes Fly very anxious. They have synthesized new clothes and weapons, but her ring is gone. To make matter worse, Sears and Roebuck have holed themselves into a sleeping chamber, dreading the coming fight on the Fred homeworld. As they continue flying through space, Fly breaks Arlene's gloom by stepping in front of her as she fired her rifle aimlessly, taking a small hit in the shoulder. At first, Arlene is worried for his safety, but then turns angry at his interference, even avoiding him for a good while until she eventually asks why he did it. When he explained that it was to "piss her off", she is again angered by eventually breaks free of her depression.
Upon reaching the Fred home world, they find nothing shy of a single Fred corpse. Recovering it and healing it, they question the Fred - a new species which the Fred calls "Newbies" in broken translation they had encountered long ago, that evolves even faster than humans, attacked them. And this new species is headed for Earth.
Unsure if this new species is a threat or an ally, Fly explores and finds one member, dead. An alien gray type creature, they revive it. However, this species evolves at a rapid pace, and tries to disable the ship, fearing what it will find when it meets the rest of its kind as several hundred years had passed since it left its planet. It attempts to get Fly and Arlene to join forces with it, but Fly kills it, not believing a word of it. Following the coordinates from the alien of where the Newbies were headed, a hundred year trip lands them on an unknown desert planet, which they've dubbed "Skinwalker". The trip takes a hundred years outside of the ship.
They find humans. Humanity, as it turned out, survived the Doom Wars. Albert lived and focused on cryogenic research, only to die before it became reality. Jill survived Los Angeles, to become an author and die of old age.
However, these humans are odd. They fear death and take no risks. And they have personality switches. Fly and Arlene, recognized as legendary heroes, are given a computer sphere to answer questions. But Fly needs one question answered to settle his suspicions, capturing the captain, they take him to the medical lab and confirm his fears - the Newbies have evolved into a microscopic entity which lives inside humans.
But humans now have no faith in anything. And Fly determines that faith is harmful to the Newbies, for unknown reasons, but his sermons on faith somehow start to cure people of Newbie infection. And he and his converted lead a battle to take the ship.
The Newbies win, however. Fly and Arlene are strapped down and with needles in their brains; their "souls" are extracted and placed into computer simulations of Phobos to examine the human soul. Realizing that the simulation feeds off memories, he changes the events, literally recruiting the first Imp to his side in a sermon, and, determined to find Arlene, recruits other monsters.
Arlene and Fly, however, wake up outside the ship. Their souls were not extracted, but merely their minds copied. The real Fly and Arlene, with their human converts and the bodies of Sears and Roebuck, escape the ship's launch rockets. Reaching their destroyed ship, medical machines revive S&R. And, as it turns out, the moon of that planet is a hollow space port.
Using a Fred escape pod to fly to the moon base, the band of survivors secure a ship, knowing that, at best, they will arrive a month after the Newbies. The Newbies, as it turns out, had not yet been to Earth, but had just encountered humans on this world. Another hundred years in real time, mere weeks to them, they reach Earth. Fly and Arlene have returned four hundred years after they last saw their home planet.
Humans survived the Doom Wars, but while signs of civilization remain, all that's left is covered in uncontrolled plant growth. No humans are found. To the rest of the survivors, it has been two hundred years to them. Flying over the United States, they reach Salt Lake City - rebuilt, and the Mormon Tabernacle bigger than ever. And even stranger, the Newbies are nowhere to be seen.
Arlene, realizing what this means, contacts the Tabernacle. Jill's mind had been copied and now operates within the building. Allowing the ship to land and them to enter, Fly and Arlene quickly meet a hologram of Jill, slightly older than when they last saw her, who explains everything.
It seems this war started six million years ago due to the Gate builder race. Twelve million years ago, this race had left behind eleven fragments of an ancient text. For the past six million years, the Klave and the Freds have been fighting a war over the interpretation of these texts, a sort of intergalactic chess game. But humans, in addition to death, also evolve faster than any other race. When the Freds encountered Earth in the 1400s, they set to motion a plan to impersonate Hell demons. But the time of the trip coupled with the time to prepare allowed centuries to pass. Humans had evolved, fought back, and ultimately won.
As to Earth, the survivors slept in cryogenic stasis, awaiting the return of the Doom heroes of legend. Jill, cloned and resting, is found. Fly and Arlene are further led to a box labeled "Albert" with a small light, presumably containing Albert's ashes.
The final chapters explain why the Newbies never arrived. The computer copies of Fly and Arlene continued through the recreations of Phobos and Deimos, building their army of "converted" demons and zombies. They find the "back door" to escape from the program.
But this door does not lead to escape. It leads to a Newbie, connected to the program. Dragging the large black slug body into the program, the fast run time of the simulation causes something unexpected - the Newbie evolves much more rapidly, until it literally vanishes. And Newbies are all linked telepathically. It appears the entire species evolved out of existence by this act.
Believing themselves to be genuine and with no way out, "Fly" and "Arlene" decide to live inside the simulation for as long as it is powered, attempting to make themselves comfortable by remembering alternate events.
 Reprinting cover images
 Key characters
Flynn "Fly" Taggart: The Doomguy, and the main narrator of the novels. Raised in Hollywood, California and Orlando, Florida by his father, who would often embarrass Fly with his crass behavior and criminal activities. Fly joined the Marines to make something of himself and escape his father's behavior. A good marine, until - as with the storyline of the games- he assaulted a superior officer who has ordered unarmed civilians fired upon. He is a non-practicing Catholic who went to Catholic school, though his religious beliefs are rather broad and he still maintains a healthy belief in God. Somewhat mechanically gifted, though sometimes lets his emotions and sense of duty override rationality.
Arlene Sanders: A female Marine who joined to prove she could be part of the Marines. Generally well respected amongst her squad for her willingness to go along with hazing rituals. She and Fly are best friends though avoid a relationship, as doing so would compromise things. She had a relationship with Wilhelm Dodd which ended when he was turned into a zombie on Deimos. She is quite intelligent and is generally more rational than Fly, though tends to be more emotional. She also tends to show a promiscuous sexual attitude towards men she likes. She was raised Episcopalian in her youth, but became a militant atheist in later years. She has problems with the Mormon religion due to her brother converting at one point in his troubled life. (Eric Harris of Columbine infamy was reported to have named his sawed-off shotgun "Arlene" , which confused some more casual fans of the series because the Marines were never actually named in gameplay, nor was there even clear evidence of different genders of Marines.)
Albert: A devout Mormon and ex-Marine who left after the killing ate away his conscious. He often looks to the Book of Mormon for guidance. He and Arlene develop a relationship though he resists her temptations. The two are married prior to their leaving for the Fred homeworld though are separated shortly after when Albert is severely wounded and can not make the trip with them. All that is known afterwards is that he recovered and returned to Earth to help humanity with the "Doom Wars" and helped the new Earth government. Albert (or a clone) was put in stasis awaiting the return of Arlene to Earth.
Jill Lovelace: A 14-year-old orphan whose parents were killed in the invasion. She appears to be loyal to the Mormon president and will say what he wants to hear, though she seems more willing to help get revenge for her parents' death than she believes in the religion and will say what people want to hear as a result. She is a skilled computer hacker. She also develops a one-sided crush on Fly. After Fly and Arlene leave Earth, Jill is forced to use poison gas to kill two human traitors, an act which does not sit well with her. What is known afterwards is that Jill survived to fight the "Doom Wars" and helped form the new Earth government and wrote history books concerning the war. When Salt Lake City was rebuilt, a copy of her mind was used as the basis for the city's computer. Jill eventually grew old and died, though her mind lived on in the computer and a clone of her was put into stasis awaiting the return of Fly and Arlene.
The President of the Twelve: The head of the Mormon religion in SLC. A cool-headed leader of the human resistance and a devout Mormon, though somewhat manipulative of those he does not trust.
The "Freds": The Earth military name for the invasion forces. An evil alien race of "deconstructionists", they plan to invade Earth by genetically altering themselves and slave races to look like creatures from Earth mythology - specifically, the Christian idea of Hell - though as a species unfamiliar with evolution, did not expect Earth to defend themselves in the several hundred years it took to organize the invasion. In their natural state, they are said to have stubby bodies with large heads resembling artichokes covered in leaf-like scales and multiple eyes. Their limbs are thin with fingers like sharp chopsticks. They are a technologically advanced race though seem to steal their technology rather than develop it. While they do naturally reproduce, they generally produce their invasion fleet through cloning vats. They are believed extinct as of the end of the series, those on Earth are all killed in the war and those on the homeworld all killed by the "Newbies" as well.
The Klave: the chief representatives of the alien forces opposing the "Freds". The Klave are a "binary" race, of which they remain in mentally linked pairs. They do not understand the concept of individuality and can not deal with individuals. The two main Klave choose the name "Sears" and "Roebuck" by mentally scanning humans to represent themselves though no specific name is ever assigned to either. Killing one half of a Klave pair will generally cause the other to stop functioning and die as well.
The "Newbies": The second race the Klave and "Freds" encounter that evolves. They were encountered by the "Freds" in the 200-year span of Fly and Arlene's trip to the Fred homeworld. In that time the Freds were wiped out by the Newbies. The Newbies eventually left that world and encountered humans, their evolution speeding up until they changed into microscopic beings that inhabit a host body. Generally mindless, and strict, they reduce their hosts to a state of fear. Strangely, whenever a host has faith in anything - a god or an idea - the Newbies cannot survive in the host anymore. Logically, chemicals produced by the body during certain emotional states may be fatal to the Newbies. All Newbies are mentally linked. It is believed their species was literally "evolved" into extinction when one linked to a sped-up computer simulation of Fly and Arlene was drawn into the program, the enhanced rate of time passage forcing it - and the rest of the species - to rapidly evolve until they vanished. Evidence of this may lie on the fact they never reached Earth as they had planned.
 Comparison with the games
The UAC facilities are described as having been built to go into the moons, which means there are no open skies as in the games, only ceilings. Green slime pools and exploding barrels remain, as do keycard doors.
The game weapons are included, with additions made. Of note is the "Sig-Cow" rifle, which is likely a reference to the rifles that the Doomguy and Troopers are drawn with in-game, despite the pistol being used as the basic weapon.
Book one follows the first game closely in terms of the plot and general locations throughout. One of the best examples is when everytime Flynn ends up in a new location (from Phobos to Deimos, then through the Hyperspace Tunnel with Arlene in tow) he loses all his equipment and is forced to use a pistol, usually the first weapon he comes across. Book two features a setting on the monsters invading Earth, but a much different story. For example, the resistance against the monsters is not unified here, as many Earth governments have turned traitor.
Book three breaks with the original plot, as contact is made with an alien race that is on humanity's side. These creatures supplied the blue soul spheres found throughout the game and the books. The main race is the Klave, whose members are found in linked mental pairs. The Klave do not understand individuality and can only interact with people in pairs. The two who accompany Fly and Arlene take the names "Sears" and "Roebuck" for themselves after scanning human minds.
Book four diverges even further from the original story, by moving Fly and Arlene into the future and introducing more aliens.
Many game levels are included, some in heavily modified forms.
- E1M1: Hangar is described in detail as Fly's entryway into the base, including the armor room and the nukage room, as well as his first encounters with zombies and imps.
- The swastika room from E1M4: Command Control is mentioned, seen by the main characters as an attempt by the demons to use symbols to scare humans, as they had previously used other symbols (e.g. upside-down crosses).
- E1M8: Phobos Anomaly is detailed with Hell Princes, the star-shaped room, and the Gate that leads to Deimos.
- E2M1: Deimos Anomaly introduces Fly to teleporters. Arlene is also found here, in the alcove with the red key card. Cacodemons are also encountered.
- Arlene is severely injured by a demon near the exit in E2M4: Deimos Lab, while she and Fly were distracted by a scrolling wall of faces also visible in the game. While approaching the exit, Fly discovers the secret room containing a soul sphere behind him, and uses it to save Arlene.
- During the period of the novel set on Deimos, the characters teleport into an area where they are surrounded by a circle of Barons of Hell, before releasing a horde of Cacodemons in to fight with them. The description of the scenario plus the reference to bodies of 'opposing' creatures in each others' lairs (including crucified bodies of the Barons) links this to the secret level Fortress of Mystery.
- E3M1: Hell Keep is easily recognizable by a good Doom player, as it is described nearly the same as in the original levels.
- E3M2: Slough of Despair is identified when one of the characters notes that the area looks like a giant hand.
- E3M9: Warrens: After passing through the part of book, which is equal to E3M1: Hell Keep, they have to fight their way through nearly the same area, but like in the game the map changes instead of teleporting out and leads to a second Cyberdemon battle.
- E3M8: Dis is the location of the first Spider Mastermind battle, with the central building in the room housing a large machine which amplifies the Mastermind's telepathy to a wider range.
- The second novel describes a battle whereby a Spider Mastermind and Cyberdemon are tricked into fighting each other. Although the scenario takes place on a train, the confrontation parallels the map Gotcha! as this is the only time in the game that the two monsters are in proximity and forces the player to cause conflict.
The monsters in the novels are not demons, but aliens engineered to look like demons (whether or not this breaks from the games is debatable, as various cutscenes in Doom II refer to them as "aliens", and Final Doom's plot has them traveling on spacecraft to reach Earth). The invading species first encountered humans in the 15th century, and had not expected such an evolutionary leap (similar to the plot of Harry Turtledove's Worldwar alternate history novels). In their natural state, the aliens are described as tall creatures with heads like artichokes covered in numerous eyes and leaves. They have long, sharp fingers like posable chopsticks. (Many of the creatures may be of other races, however, subjugated and cloned for an army.) Some creatures seem to have a natural hatred of others, exemplified by the fact that Barons and Cacodemons willingly kill each other.
The monsters are often referred to by new names by the characters. The exceptions are the Imps, as well as one scientist character who uses the proper game names. His reasoning behind the names is that they are "creatures from the id".
- Former Humans: Dead humans reanimated through a chemical introduced to their bodies after death. The chemical was likely developed by the aliens though human traitors on Earth were allowed to produce it in exchange for basic freedoms. Unlike zombies in either films or other games, the undead here show no interest in consuming living flesh, but rather attacking living humans with whatever weapon they have. Soldiers killed in battle will carry their guns and fire until out of ammo, while civilians will use whatever they were holding when they died. They have limited reasoning functions though they seem obedient to the demons either by chemical programming or through telepathy. Certain soldier zombies Flynn comes across talk in a repetitive, "tape loop" way, usually babbling about "the Gate is the key". They have what is often described as a "sour lemon" smell with eyes that are dried from non-blinking. Flynn and the other humans at one point obtain rotten lemons and coat themselves with them to smell the same and infiltrate a demon stronghold. Called simply "zombies" in the series.
- Imp: Unchanged in appearance for the most part, though their eyes are described as "maddened red slits" versus the large, hateful eyes in the game. Some can talk, and their speech usually consists of simple sentences with long, drawn-out hisses for the letter S. Much like in the game, they usually hiss when alerted, but can also roar when attacking or injured. Their fireball-throwing ability is explained by having them spit a wad of mucus into one hand, which ignites on contact with the air and is then hurled. They are covered in an oily substance which protects them from their own flaming mucus. Called "spinies" in the series.
- Chaingunner: Very different from the game versions. They are not zombies, but living humans who all look identical (possibly a reference to the usage of a single sprite set in-game to represent numerous copies of an enemy). Instead of a traditional chaingun, they come armed with belt-fed machine guns. They are believed to either be clones or human traitors who have been genetically altered. In addition to their armor and gun, they wear night-vision goggles. Called "Clydes" in the series"
- Demon: Unchanged in appearance, but found in various sizes. They make a pig-like snuffling sound and are similar to their depiction in the games as rather brutish, stupid beasts who closely resemble guard dogs in intelligence and behavior. They are also said to have an extremely foul body odor. Called "pinkies" in the series"
- Spectre: Invisible "ghosts" appear primarily in the Phobos installation and are at first difficult to determine. They appear with a "shimmering", "watery" appearance and apparently do not bleed when shot at. They make the same pig-sounds as the "pinkies" when Flynn comes across them in his battle with the hell-princes, leading to the conclusion that they and the pinkies are "one in the same". Called "ghosts" in the series.
- Lost Soul: Though unchanged in appearance, they are instead mechanical flying skulls on fire. They still explode when killed, but as a result of a fiery combustion of jet fuel. Called "flying skulls" in the series.
- Cacodemon: Unchanged, with the exception that they are found in various sizes. They are referred to by the characters as 'Pumpkins,' and have an uncontrollable hatred of Barons of Hell. In the computer simulation of Phobos in "Endgame", Flynn somehow "remembers" that they can talk, and the one he befriends, "Olestradamus", possesses a voice that sounds like "Darth Vader on a tape running at half speed" and with a stutter.
- Mancubus: Unchanged in appearance and behavior, though they come in various sizes. It is explained that their body fat and loose skin causes their eyes and ears to be almost completely covered, leaving them nearly deaf and with poor eyesight. They are believed to be an early attempt at human cloning. They are nick-named 'Fatties' by the characters. The guns mounted on their arms are described as having three smaller mouths that shoot out white phosphorous versus the single, large barreled guns in the game.
- Arachnotron: Does not appear, though Marines on Earth mention having encountered them in battles. They are referred to as "spider-babies".
- Revenant: Nearly the same as in the games, but appear to have a layer of skin on their bodies, much like the Revenant of Doom 3. They also wear red shorts and a white T-shirt (most likely due to the authors misinterpreting the Revenant's in-game sprite and mistaking the body armor and gore on its legs for clothing). They are believed to be an early attempt by the aliens to genetically grow human duplicates, albeit a failed one. The fact they wear clothes when none of the other monsters do may back up this belief. They possess the same broken marionette walking trait and up-close punch, but their missile launchers only have two missiles loaded. More often than not, the firing of the missiles destroys the revenant. They are nick-named 'Bonies' by the characters.
- Pain Elemental: Appears once; looks and behaves as in the game. Called a "superpumpkin" in the series. As our heroes are battling the creature, the lighting in the corridor they're in begins to shift, from regular light, to blue, and then red, distracting and confusing the characters; this effect subsides after the Pain Elemental is destroyed. Flynn wonders if the "superpumpkin" was the cause of the bizarre light.
- Arch-Vile: These are simplified in the novels. They are not shown to resurrect the dead (though neither is it specifically stated that they do not have this ability), and instead of creating a wall of flame, they contract their bodies and explode, like a living bomb, setting anything around it on fire. They are also surrounded by intense heat, enough to melt bullets shot at them. An ordinary fire extinguisher can disable them for a few minutes, however. They are nick-named 'Fire Eaters' by the characters.
- Baron of Hell: Unchanged in physical form, but fire their plasma from mechanical wrist launchers (as with the game's cover art). They are called "hell princes" by Flynn.
- Spider Mastermind: Almost identical to the game versions. Their brain cases are protected by clear domes, and they can also use telepathic attacks to induce fear in humans. They also appear to have the ability to speak perfect English, though the one on Deimos only did so to Bill Ritch during his interrogation and never to anyone else. While the Doom manual seems to identify the main Mastermind as female, all indications in the novel are that it is male - though no real identifier is ever given aside from human assumption. Others are later encountered on Earth. Strangely, the book seems inconsistent in its wording, as at one point it is mentioned they have six mechanical legs though other mentions seem to follow the game design. It was once theorized by Flynn and Arlene that the Mastermind had only a tenuous control over the invading forces on Phobos and Deimos, and that left to their own devices, they would kill each other, though they were not able to know for sure after killing it. It's referred to as the "spidermind" in the series.
- Cyberdemon: Described as being fifteen meters tall and has a rocket launcher powered by JP-9 rocket propellant. They are unchanged in physical appearance for the most part, with the exception of a visible missile rack on their backs. One character manages to disarm a Cyberdemon by sabotaging the inner mechanism of this missile rack. Called a "steam demon" by Flynn, a "cyberdude" by Bill Ritch, and a "Moloch" by Albert.
In addition to the game's monsters, a mysterious creature is also introduced at one point, a black cloud-like creature that stays near water, with three shark fin-like protrusions on its head. The only one seen is killed, evaporating as its core is destroyed by a bullet. It is never named, nor is its nature explained.
The Doom novels have been heavily criticised by some members of the Doom community. Much of the criticism comes from the ways the story differs from the game.
While the story is set in the Doom universe, the authors take several artistic liberties. The novels also introduce several other characters not suggested by the video games, with many character traits and religious/political ideas which are clearly author self-inserts (also known as "Marty Stu" or "Mary Sue" characters).
Beginning with Infernal Sky, the storyline departs dramatically from anything related to the computer game, becoming more reminiscent of science-fiction space operas such as The Forever War.
There are a few continuity errors in the series as well: e.g. the differentiation of the Spider Mastermind's physical appearance (most noticeably having a crystal dome over its brain); Gunnery Sergeant Goforth having a "thick, Georgian drawl" ("Knee-Deep in the Dead") but seems to come from South Carolina ("Endgame"); Arlene being the one to dub the imps as "imps" while Flynn called them "spinies" in "Knee-Deep in the Dead", though in "Hell on Earth" Arlene claims that "I can see why Fly calls them 'imps'", an incorrect assumption that he called them as such first ; Flynn's assumption that, in order to secure "Dude" Dardier's shotgun in "Knee-Deep in the Dead", he would have to "put a bullet into her pretty blond head" should she come back as a zombie, but when he comes across her corpse later in the book, she is, for whatever reason, a red-head; some confusion as to which monster killed Hidalgo's wife in "Infernal Sky". He originally states that it was a minotaur, leading some readers to believe it to be a baron (in the books, they are usually referred to as "minotaurs"), but other characters later in the book claim that it was, apparently, a cyberdemon.
Flynn Taggart's serial number is 888-23-9912.
 ISBN numbers
- Doom: Knee-Deep in the Dead - ISBN 0671525557
- Doom: Hell on Earth - ISBN 067152562X
- Doom: Infernal Sky - ISBN 0671525638
- Doom: Endgame - ISBN 0671525662
 See also
- This article incorporates text from the open-content Wikipedia online encyclopedia article Doom novels.
- This article incorporates text from the open-content Wikipedia online encyclopedia article Doom spin-offs and homages.
- The Page of Doom's image gallery (see first & second image row for scans of the novel covers)